Panoramic receiver bandpass compensation system



PANORAMIC RECEIVER BANDPASS COMPENSATION SYSTEM Filed sept. 19, 1945 E. E. HERMAN Feb. 9, 1954 2 Sheets-Sheet l Feb. 9, 1954 2 Sheets-Sheet 2 Filed Sept. 19, 1945 W Ig Patented Feb. 9, 1954 UNITED NSTATES PATENT F'ANQRAMIC RECEIVER BANDI-'ASS `Elvin E. Herman, Washington, '.D. v(J. @causative sente-,mbar 1.9, 19.45. Serial @3159.5

19 Glaimws.

,(Gtantcsi anger Title 35, 379,19 ,(4952), 266) vice such a way .as to .compensate vfor requency selectivity in circuits in or coupled to the device.

It isanotherlobjectof the invention to .providea means .of fbandpass. compensation that is `readily adjustable to .compensate dor idiierent `.torloit011s u Another .object .is to provide ia ,means rofbandfypass'compensation in which .the amount ocomr pensation varies automatically .as ,the l.vvidtic of spectrum vswept -is changed.

-Sti11 ra 'funtherobject .iis to .proyideia means of #bandpasscompensatonfifor a visualifrequenqy scanning .device .which -iresults .in visual signals fpresented being .more nearly.` proportional to -sig- Y-nal strength at..=the `.receiver .antenna than .in vprior art ldevices. i

The invention will be further understoodwth reference to the exemplary embodiment shown Iin'thedrawing l in which:

iFig; 1 showsfpartly ineblock .iandpartlyiincircuit `diagram a` frequency.scanning.devicefincolf porating the invention.

Fig. Zshows partly in.b1ock andpartiy.. in.. circuit vldiagram another. enibodimentnofstheinventon.

Fig. 3 shows Wave 1forms.deve1opedJoy theicirj- -cuitof Fig. .2.

The block 'diag-nammortion v of Figure 1 mepree Y-sents a frequency :scanning device ...with ...visual epresentation l--and the .circuit diagram .portion represents a .means :for `supplying .l a .fbias .voltage to -beiused vary-ing. the. gain .i :of sthe..deviioe...to

compensate for frequency selective circuits. .'Ihe

vvscope of `the invention Visnnot: -1imitedft0.,.a visual type-of presentatiomnhowever.

, `In such` a l device,i.fradio .frequencytsignals ...are i-ndicated.-on tithe: screeninfo-cathoderay atubeibfy Vertical deflection pips, and the horizontalgdis- `Z placement of the finies ndate ,the difference between ,the signal;

quency, Vit is ,necessary that .the .input lilrlay band ne scanned as ine .cathode raytub sweeps `norizcnialiv thescren- As the frequency band is swept, ntlie gain 1 of the .amplifier .changed .t9 comp Vfrequency ,selectivity `Qf zh? .DylQliS 4, circuits .and/or of .the .amnliferr, or

quired is for.previoussolcctivecir ts.

In Eig. .1, .thaselectively ed signal in# .put l isedthrouehthe-an1n1ieri2 tothe @hier 3, Where it beats with .the V output Aof the i local swept oscillator A'. The frequency rof the sci'ly `later Avarieswith time. andhence ,the ,1.- .put of the ,mixer `...will be .series "of ,gnam whose .timenf .annearance danendaon inequality- `The,mixeroutput fis amplified inthe dI.'i'. ani 1ifier 5, and demodulated in detector 6. The W 4m1 output. of` the `detector .is .ftedtnransh amplifiers .1 and 1 and applied .to ...the vertical ...deitiestion plates of cathode ,iaytuloe 9.

A saw tooth sweep voltage vis Droguerie@ :.ipthe `,generator I0 ,andappliedthrougnx npiiiieijs Ll and lzto the.norizantalnlatesf G1R-b1195219- Tnis sweep.vQ1tagenauses `the .beam of tls@ cathode raytube .to move ,hoi 1A ntaiiymacross the Screen `as the signals, W1Q-Satir1 .Qf apneagane .e5 depends on frequency, are applicato the Mertqal deflection .platesrnnis is thet.tasafiscalitethe` sweep valise@ .is also employed to vary .the f nancy, @fthe ylocal .swept oscillator. @Hence/the mef aplaaal sonant clrcuit most applications. :the nnly compensatie laccaeos tionally to time, the gm of the reactor tube changes proportionally to time, injecting into the tank circuit of the oscillator a reactance proportional to time, which causes the frequency of the oscillator to vary proportionally to time.

The length of the time base of the C. R. tube and the frequency range of the swept Voscillator can be varied together by changing the gain of amplifer Il with amplitude control l5. The frequency range of the swept oscillator 4 can be varied independently of the time base of the C. R. T. by the scanning width control i3.

The output of the local swept oscillator 4 is used also to supply the bias voltage for the band pass compensation. rlhis output is fed to grid 2l of amplifier 22, which in addition to its arnplifying action isolates the local oscillator 4 from the tank circuit 23 and also may act as a limiter. Circuit 23 is tuned to the center frequency of the local oscillator by variable inductance 24.

' The amplified output of oscillator 4, which varies from a point below center frequency to an equal point above center frequency, is selectively attenuated by the tank circuit 23. rThe diode 25 rectiiies the selectively attenuated out put of amplifier 22 and applies it as a negative biasing voltage to the grid of one or more of the tubes in amplier 2. It is to be understood that this bias may be applied to the I.F. amplier or the mixer as well as to ampliiier 2 or to any combination thereof.

The waveform of the bias voltage will follow a normal frequency selectivity curve whose shape depends on the Q of the tuned circuit. Hence, at "a point below center frequency, where the amplitude of the input l is low, the negative bias applied to the amplifier from diode 25 will be low. At a point near center frequency where the amplitude of the input is high, the bias of `amplifier 2 will be high. At a point above center frequency where the input amplitude is low the bias will be low. Hence the gain of amplifier 2 is varied in such a way as to compensate for the selectivity of the amplifier and of previous cir cuits.

Diiierent conditions of circuit selectivity require variation of both the shape and the overall amplitude of the bias waveform.

The effective Q of the tuned circuit can be varied by adjusting potentiometer 25, thus changing the compensation bias wave shape. The potentiometer could be placed between condenser 21 and Contact 28 instead of as shown. Potem tiometer 25 is used to adjust the overall amplitude -of the bias waveform.

When the local oscillator sweeps over a smaller frequency range, due to lower setting of control I3, less bandpass compensation is needed. Since the compensation waveform is derived from the local oscillator output, this correction takes place automatically. A smaller excursion of the oscillator frequency, for example, results in smaller overall amplitude change in the bias waveform.

It will be noted that in effect the voltage variation of the sweep generator l5 was shaped to produce the band pass compensation, since the `sweep voltage varied the frequency of the local 4gain of the panoramic device.

4 values so chosen as to give a gain of unity. The circuit is also designed so that when zero signal appears at grid 42 of tube 4I, the cathode to ground voltage across resistor 43 of tube 4| equals that across resistor 44 in the cathode circuit of tube 45.

The voltage from sweep generator l0 is fed through amplifier Il and potentiometer I3 to grid 42 of tube 4I.

Let the voltage across resistor 43 be E for no signal at grid 42. The voltage across resistor 44 is also E. If the voltage across bias source 46 is also set at E, then no appreciable currents iiow in the two diodes 4l and 48 for the plate voltage of each diode equals its cathode voltage.

If now, the sweep voltage is introduced at grid 42 of tube 4|, this grid will vary uniformly from a valuer below average bias to an equal value above average bias during each cycle as shown by waveform 5I of Fig. 3. The voltage at grid 55 of tube 45 will be as shown in waveform 52 since the gain of tube 4l is 1.

As the voltage at grid 42 changes from a value below average bias up to average bias, the voltage across cathode resistor 43 will vary from a value below E up to E. Tube 41 will not conduct since its plate is always below E and its cathode is E. Tube 4'! then develops no voltage across resistor 53 in this interval.

During the first half cycle, however, the grid 50 of tube 45 varies from a value above average bias to average bias causing the voltage across cathode resistor 44 to vary from a value above E to E. Since this causes the plate of diode 48 to be above cathode voltage E during this half cycle, the diode will conduct producing a voltage across resistor 53 as shown in the rst half of waveform 54. The curvature is due to the non-linearity of the diode characteristic. (Tube 41 was cut off and the voltage across resistor 53 due to conduction of tube 48 helps keep it cut off.)

During the second half cycle, the voltage at grid 42 varies from the value of average grid bias to a value above average grid bias and the voltage across cathode resistor 43 will rise with it from a value E to a value above E. Diode 41 will conduct increasingly producing across resistor 53 the other half cycle of waveform 54. y

Tube 48 is cut oif during this half cycle, as its plate voltage is always lower than its cathode voltage. Since grid 55 goes from average bias to value below it, the voltage across resistor 44 goes from E to a value below E. The cathode of 48 is always at E or abovel and hence tube 48 cannot conduct.

If bias source 45 is raised to a value greater than E, each diode will conduct a smaller portion of its conducting half cycle giving a voltage across .resistor 53 as shown in waveform 55.

Hence we see that by changing the value of bias voltage 46, we can change the shape of the compensation pattern to be applied to vary the By varying the potentiometer 53, the amount of compensation voltage can be varied.

If the scanning width control I3 is turned down so that frequency range swept is less the amount of compensation will be less, due to the smaller positive and negative excursion of the sweep voltage.

If the diode characteristic` is not such as `to properly shape the compensation bias voltage, shaping circuits 52. may be employed to shape 'the waveform as desired'before applying it to ampliier2..

enteros' The invention has "the following features:

Bandpass compensation is attained by applying a biias voltage to vary 'the gain ofthe device in ituverse ratio to 'the selectivity .of theluput circui s.

Theshape .of .the bias voltage can "be easily varied to `compensate `for different conditions of receiver selectivity.

The amplitude of the bias voltage Vcanbe varied to adjust for variationin selectivity requirements.

The minimum gain point (or center of compensation) can .be varied to adjust for variation in center frequency.

The amount .of compensation automatically Changes as the Width of the frequency band swept changes.

'It will "be understood that the specific embodiments described above are exemplary only, and that the scope of the invention will be determined with reference to the appended claims.

The invention described herein may be manufactured and used 'by or for the Government of the United States of America for governmental purposes Without the payment of any royalty thereon or therefor.

What is claimed is:

'1. In a frequency scanning device including an amplifier providing a selectively attenuated frequency band, an oscillator, means operative to vary the,` frequency of "the oscillator periodically through a predetermined band of frequencies, means mixing the outputs of the amplifier and the oscillator, `means attenuating the oscillator output according to a predetermined frequency selectivity curve, means obtaining the envelope of `the attenuated output, and means applying the voltage envelope as a bias `voltage to said ampliher- 2. In combination, `an amplifier for a selectively attenuated frequency band, frequency sweep means including oscillator means operative to produce an output the frequency of which 4varies periodically through a predetermined band of frequencies and means mixing the amplifier output and the varying frequency output, a resonant circuit energized hy the varying frequency output of said oscillator means for producingan output having a predetermined frequency selectivity characteristic, means detecting the output of said circuit and utilizing the resultant voltage to vary the gain of said amplifier in .inverse ratio to the selectivity characteristic of said frequency band.

In combination, an amplifier for a selectively attenuated frequency band, frequency sweep means including oscillator means ,Operative to produce an output the frequency of which varies periodically through a predetermined band of frequencies and means mixing the amplifier output and the varying frequency output to `produce an intermediate frequency output, oscillographic means operable in synchronism with said frequency sweep means for producing an indication of said intermediate frequency output, a resonant circuit energized by the varying frequency output of said oscillator means for producing an output having a predetermined frequency selectivity characteristic, means detecting .the output of said circuit and utilizing the resultant voltage to vary the gain of said amplifier in inverse ratio to` the selectivity characteristic of said Vfrequency band.

e, In combination with a mixer, .an oscillator coupled to said mixer and an amplifier feeding a selectively attenuated frequency band to 'said mixer, `the selectivity characteristic of said frequency amplifier lacing in the l'form of a hmm), cyclic sweep means including a saw-tooth wave generator for varying the frequency of said oscillator periodically through a predetermined band of frequencies .in synchronism with said 'cyclic sweep means, means shaping the saw-tooth wave output of said generator for producing a voltage waveform 4varying the rgain in inverse ratio to the selectivity characteristics of said frequency band and means applying .said voltage waveform to vary the gain of said amplier.

5. In a device for scanning a selectively 'attenuated frequency hand, the selectivity characteristicsbeing in the form of a hump, means cyclically scanning the frequency band, means for varying the gain of the device to compensate for selectivity characteristics of said frequency band comprising means operable 'in synchronism with scanning of the band and producing a bias voltage varying 'in inverse ratio to said selectivity characteristics an-d means' employing said voltage to vary the gain of said device.

6. 'In a device for scanning a selectively attenuated frequency band, the iselectivity characteristics being in the form of a hump, means cyclically scanning the frequency band, `means operable in synchroni'sm with scanning of the hand for producing a bias voltage fed to the device 4to vary the gain thereof, and lmeans adj-usting the waveform of the bias voltage 4to vary the gain of the device in inverse ratio to saidselectivity characteristics of the frequency hand.

7. In a device for scanning a selectively attenf uated frequency band, the selectivity characteristic being in the form of a hump, vmeans cyclically scanning the frequencyy band, a bandpass compensation system comprising mea-ns operable synchronism with scanning of the -band lfor `pro-` ducing a bias voltage fed to the device to vary the gain thereof, means adjusting the waveform of the bias voltage to vary the gain of the device in inverse ratio to said selectivity characteristic of the frequency band, and means -operativeto adjust the overall amplitude of the bias voltage.

. ln a device for scanning a selectively attenuated frequency band, the selectivity character-- istic being in the form of a hump, means ycyclical-- ly scanning thefrequency band, a bandpass compensation system comprising means Voperable in synchronism with scanning of the band for producing a bias voltage fed to the device to vary the gain thereof in inverse ratio to said selectivity characteristic of the frequency band, and means operative to control the bias voltage lresponsively to varationsin frequency range being scanned for varying the amount of compensation.

9. In a device for scanning a selectively attenuated frequency hand, a bandpa-ss compensation system comprising means operative in synchronism with scanning of the hand to supply a loias voltage fed to the device to vary `the gain thereof, means adjusting the waveform of the bias voltage to vary the gain of the device in inverse ratio to the selectivity characteristic of the frequency band, and means for shifting the waveform ofv means-shaping the saw-tooth output of the generator to provide a voltage waveform varying the gain in inverse ratio to said selectivity characteristic of the frequency band, and means applying said voltage to bias the amplifier in synchronisrn with the cyclic sweeping of said variable frequency oscillator.

il. In combination, an amplifier for a selectively attenuated frequency band, the selectivity characteristic being in the form of a hump, means cyclically scanning the output of the amplifier, circuit means producing a control voltage having a Waveform corresponding to said frequency selectivity characteristic of the frequency band, means utilizing the control voltage to vary the gain of the amplifier in inverse ratio to said selectivity characteristic of the frequency band and means establishing synchronous operation of the Scanning means and the circuit means.

12. An amplitude stabilization system comprising the combination of a radio receiver circuit having a non-uniform radio frequency response curve over the band of frequencies to be received, a signal transmission vpath coupled to the output of said receiver circuit for relaying the signals therefrom, the transfer efciency of said path being inversely proportional to the magnitude of a control voltage fed thereto, a resonant circuit xedly tuned to a rst frequency, a source of variable frequency voltage coupled to the input of said resonant circuit, means coupled to said voltage source for periodically varying said voltage source above and below said rst frequency, and means coupled between the output of said resonant circuit and said transmission path for developing a control voltage Whose magnitude is proportional to the amplitude of the alternating Voltage variations developed in said resonant circuit by said source of variable frequency voltage and for coupling the control voltage to said path to control the transfer efficiency thereof.

13. An amplitude stabilization system comprising the combination of a radio receiver circuit having a radio frequency response curve which varies in the same direction on either side of a first given frequency, a rst radio frequency amplier coupled to the output of said receiver circuit whose gain is inversely proportional to the magnitude of a control voltage fed thereto, a resonant circuit fiXedly tuned to a second frequency, a source of variable frequency voltage coupled to the input of said resonant circuit, means coupled to said voltage source for periodically varying the frequency of said source above and below said second frequency, a rst means coupled between the output of said resonant circuit and said amplifier for developing a direct current control voltage Whose magnitude is proportional to the amplitude of the alternating voltage variations developed in said resonant circuit by said source of variable frequency voltage and for coupling the control voltage to said radio frequency amplifier.

14. An amplitude stabilization system comprising the combination of a radio receiver circuit having a radio frequency response curve which varies in the same direction on either side of a rst given frequency, a first radio frequency amplifier coupled to the output of said receiver circuit whose gain is inversely proportional to the magnitude of a control voltage fed thereto, a resonant circuit xedly tuned to a second frequency diiferentrfrom said first frequency, a source ofvariable' frequency voltage coupled to the input of said resonant circuit, means coupled to said voltage source for periodically varying the frequency of said source above and below said second frequency, a first means coupled between the output of said resonant circuit and said amplifier for developing a direct current control voltage whose magnitude is proportional to the amplitude of the alternating voltage variations developed in said resonant circuit by said source of variable frequency and for coupling the control voltage to said radio frequency amplifier, a second means coupled to said amplifier output and to said source of variable frequency voltage for heterodyning the frequencies thereof, a third means tuned to one of the heterodyne frequencies coupled to said second means.

15. An amplitude stabilization system comprising the combination of a radio receiver circuit having a radio frequency response curve which varies in the same direction on either side of a,

first given frequency, a rst radio frequency amplifier coupled to the output of said receiver circuit Whose gain is inversely proportional to the magnitude of a control voltage fed thereto, a resonant circuit ii'xedly tuned to a second frequency, said resonant circuit including a variable resistance means, means for varying said resistance means whereby to vary the sharpness of the selectivity curve of said resonant circuit, a source of variable frequency voltage coupled to the input of said resonant circuit, means coupled to said voltage source for periodically varying the frequency of said source above and below said second frequency, a first means coupled between the output of said resonant circuit and said amplifier for developing a direct current control voltage whose magnitude is proportional to the amplitude of the alternating voltage variations developed in said resonant circuit by said source of variable frequency voltage and for coupling the control voltage to said radio frequency amplifier.

15. An amplitude stabilization system comprising the combination of a radio receiver circuit having a radio frequency response curve which varies in the lsame direction on either side of a first given frequency, a rst radio frequency amplier coupled to the output of said receiver circuit whose gain is inversely proportional to the magnitude of a control voltage fed thereto, a resonant circuit nxedly tuned to a second frequency, a source of variable frequency voltage coupled to the input of said resonant circuit, means coupled to said voltage source for periodically varying said source above and below said second frequency, a rst means coupled between the output of said resonant circuit and said amplier for developing a direct current control voltage Whose magnitude is proportional to the amplitude of the alternating voltage variations developed in said resonant circuit by said source of variable frequency voltage and for coupling the control voltage to said radio frequency amplier, a second means coupled to said ampliiier output and to a source of periodically varying frequency voltage for heterodyning the frequencies thereof, a third means tuned to one of the heterodyne frequencies coupled to said second means.

17. In combination, a receiver having an input circuit, said input circuit having unequal sensi tivity to different signals in a frequency band, a gain adjustable frequency scanning spectrum analyzer for analyzing and visually displaying the amplitudes of signals received by said input circuit, and means for varying the gain of said spectrum analyzer in synchronism with said frequency scanning during said frequency scanning so as to compensate for said unequal sensitivity of said input circuit to different frequencies in said frequency band.

18. In a device for scanning a selectively attenuated frequency band, a band pass compensation system comprising means operative in synchronism with scanning of the band to supply a bias voltage fed to the device to vary the gain thereof, means adjusting the waveform of the bias voltage to vary the gain of the device in inverse ratio to the selectivity characteristic of the frequency band, and means for shifting the waveform of the bias voltage to maintain the maximum amplitude of the bias voltage coinci dent with the center frequency of the frequency band.

19. In combination, a source of a selectively attenuated band of signals havingunequal attenuation at diierent frequency positions of said band, a gain adjustable frequency scanning spectrum analyzer for analyzing and visually displaying the amplitudes of signals in said band, and means for varying the gain of said spectrum analyzer in synchronism with said frequency scanning during said frequency scanning so as to compensate for said unequal attenuation of different frequency positions of said band,

ELVIN E'. HERMAN.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,935,401 Kenney Nov. 14, 1933 2,245,365 Riddle June 10, 1941 2,323,376 Harvey July 6, 1943 2,371,397 Koch Mar. 13, 1945 2,412,991 Labin Dec. 24, 1946 

